The present invention relates generally to plasma cutting systems and, more particularly, to a method and apparatus for localized feedback and control systems. Specifically, the present invention provides a system and method of controlling a plasma cutting process by localizing feedback sensors and a processing unit within a plasma-cutting torch.
Plasma cutting is a process in which an electric arc is used to cut a workpiece. Plasma cutters typically include a power source, an air supply, and a torch. The torch or plasma torch is used to create and maintain the arc and plasma that perform the cutting. The plasma cutting power source receives an input voltage from a transmission power line or generator and provides an output voltage to a pair of output terminals, one of which is connected to an electrode and the other of which is connected to the workpiece.
The air supply is used with most plasma cutters to help start the arc, provide the plasma cutting gas to the torch, and cool the torch. A movable or fixed electrode serves as a cathode and a fixed nozzle serves as an anode. The air supply moves the electrode and as the electrode moves away from the nozzle, it opens the nozzle, and a plasma jet is created. The plasma jet causes the arc to transfer to the work piece, and thus initiates the cutting process. In other plasma cutting systems, a high frequency starter is used to initiate the cutting process.
The power source is typically supplied with operational feedback from the torch and a processor, disposed in the power source, interprets the data and controls the operation of the power source and the plasma cutting process accordingly. For example, the processor in the power source is provided with feedback about the position of the torch trigger and whether all necessary torch components are securely in place at the torch. From the feedback, the processor determines whether to initiate cutting, pause cutting, discontinue cutting, or augment the operation of the plasma cutter during cutting.
This feedback is typically provided via dedicated communications lines. Therefore, for each form of feedback that is sent from the torch to the power source, an individual communications line is connected between the power supply and cutting torch. Therefore, a parallel communications system is utilized to send feedback from the cutting torch to the power source whereby a processor disposed within the power source controls the operation of the plasma cutter accordingly. However, this system presents numerous drawbacks.
First, plasma cutting is a high voltage process and therefore the user must be mindful that precautionary measures must be taken to avoid improper operation. As such, it is necessary to determine whether specific conditions are present prior to the initiation of cutting. For example, before the power source responds to a request for operational power at the torch, the processor of the power source typically determines whether a retaining cup, fastened at the torch tip and securing the electrode, is in place. This ensures that the torch is in operating condition prior to cutting. However, while it is common to provide a cup-attached signal before permitting operational cutting, additional feedback is limited by the number of communication links between the feedback system located in the torch and the processing unit located in the power source. Specifically, since the feedback must be sent from the torch to the processor located in the power source, the feedback must travel over a lengthy cable connecting the torch and the power source. To control manufacturing costs and maintain portability of the plasma cutter, it is desirable to limit the number of communications links from the feedback system of the torch to the power source. As such, though additional sensors could be included to provide additional feedback regarding the plasma cutting process, the number of sensors to provide feedback is limited by the number of communications links.
Second, such systems are dependent upon the power source for operational control. That is, though operational feedback is gathered at the torch, the torch is dependent upon the power source for all processing and control commands. As a result of this dependency, when replacements or upgrades to the control system are desired, it is necessary to replace the power source, and often necessary to replace both the power source and the torch. Therefore, incremental upgrades are generally cost prohibitive.
It would therefore be desirable to design a plasma cutting system that is capable of controlling a plasma cutting process with increasing portability and interchangeability. It would also be desirable for the plasma cutting system to be incrementally upgradeable. Specifically, it would be desirable to design a plasma cutting system having localized feedback and control.